compression dropping
08-11-07, 03:59 PM
#1
compression dropping
So yesterday my compression was 45/45/45 on both rotors (12A), and now it's 30/30/30 on my front rotor (havn't checked rear rotor). Why would I loose 15psi of compression so fast, and so evenly accross all the rotors? The only thing that I've done today was 2 quarts of H2O for the water treatment, and 1/2 can of SeaFoam through the carb.
08-11-07, 09:04 PM
#7
FB+FC=F-ME
Well,if you did succesfully decarbonize the rotors,then the compression ratio would drop due to the now larger combustion space in the bathtubs.The water injection method works,no doubt......but it cant soak into the apex and side seal grooves to really soften up and remove all the carbon that affect the seals ability to do their job.
Seafoam can do that,but you have to give it time to work and you have to flog it afterwards to really get the crap out.Thats why many people preffer the ATF soaking trick.ATF is cheap and you can let it sit overnight or for days while it marinates and gets things unstuck.Then,start it up,blow it out and try again if you need to...all for pennies.
There is always the chance that your housings/seals are truely shot and no amount of chemicals/decarbonizing is going to raise the compression.Lowering the compression by decarbonizing the rotors is usually a good thing,provided the seals are still doing their job.If they arent,its not going to help much to remove carbon using the water method.
Seafoam can do that,but you have to give it time to work and you have to flog it afterwards to really get the crap out.Thats why many people preffer the ATF soaking trick.ATF is cheap and you can let it sit overnight or for days while it marinates and gets things unstuck.Then,start it up,blow it out and try again if you need to...all for pennies.
There is always the chance that your housings/seals are truely shot and no amount of chemicals/decarbonizing is going to raise the compression.Lowering the compression by decarbonizing the rotors is usually a good thing,provided the seals are still doing their job.If they arent,its not going to help much to remove carbon using the water method.
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08-11-07, 09:14 PM
#9
also, i'm pressurizing the **** out of my oil sump. check out my other thread about that.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/oil-spewing-out-filler-neck-678923/
https://www.rx7club.com/1st-generation-specific-1979-1985-18/oil-spewing-out-filler-neck-678923/
08-11-07, 11:50 PM
#13
Great Scott!
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are you doing this with a cold engine or a engine that has reached operating temp... I have one that has near perfect factory compression that tested low a long time ago when I did my first test... I freaked out until my friend laughed at me and told me to let the engine warm up...
08-12-07, 10:46 PM
#17
Great Scott!
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Who knows... I've just heard bad things about it so I steer clear from it unless all other options have been exhausted...
08-13-07, 12:19 AM
#18
i did the ATF trick in my first rx7. it worked wonders. the car pulled hard due to teh compression being back. i just put too much in there so every time the car would backfire thered be a huge smoke screen. i wouldnt recommend it for the first choice due to the oil rings, but in a last resort case, as yours is, do it. i prefer sea foam.
08-13-07, 12:55 AM
#19
FB+FC=F-ME
I never had any issues using ATF in my junkyard engines.
I even let my old 13B 4-port sit for weeks with ATF in it before I installed it.That engine ran like a raped ape for years and never puffed a single cloud of smoke.....its still on the road as far as I know,I sold it to RSdevil along with my Yaw carb back in 01'.
Ive no doubt that plenty of engines have started having problems after an ATF treatment.....but there are usually problems present before the treatment is even attempted.If ATF loosens the gunk,and the gunk is the only thing holding the oil back....you can hardly blame the ATF for the results.The engine needed attention beyond a decarbonizing in such a case.Show me proof positive that the ATF caused/contributed to the failure(s) and Ill change my opinion of the stuff.
I even let my old 13B 4-port sit for weeks with ATF in it before I installed it.That engine ran like a raped ape for years and never puffed a single cloud of smoke.....its still on the road as far as I know,I sold it to RSdevil along with my Yaw carb back in 01'.
Ive no doubt that plenty of engines have started having problems after an ATF treatment.....but there are usually problems present before the treatment is even attempted.If ATF loosens the gunk,and the gunk is the only thing holding the oil back....you can hardly blame the ATF for the results.The engine needed attention beyond a decarbonizing in such a case.Show me proof positive that the ATF caused/contributed to the failure(s) and Ill change my opinion of the stuff.
08-13-07, 02:02 AM
#22
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Well said Steve. ATF does have chemicals to soften rubber seals. However, they are not in such high quanities to to adversely affect the oil o-rings that badly.
Heck, I have used ATF (1 qt to an oil change) added to the crankcase of piston engines to help stop smoking and oil consumption after they had sat for a few years. It's amazing how well that stuff works. I had one engine I done that to, and 5 years later, almost 100K, it was still running fine, and had very little oil consumption.
I have one 12A that tends to give off a smokescreen when reved to over 6K. I'm tempted to try the ATF in the crankcase of it. Can't make it any worse......
Heck, I have used ATF (1 qt to an oil change) added to the crankcase of piston engines to help stop smoking and oil consumption after they had sat for a few years. It's amazing how well that stuff works. I had one engine I done that to, and 5 years later, almost 100K, it was still running fine, and had very little oil consumption.
I have one 12A that tends to give off a smokescreen when reved to over 6K. I'm tempted to try the ATF in the crankcase of it. Can't make it any worse......
08-13-07, 02:41 AM
#23
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Should have just run the Seafoam through a partial tank of gas. That will get you the best results every time in my opinion...
Rogue Wolf; check out Lucas for your smoking issue....
Rogue Wolf; check out Lucas for your smoking issue....
08-13-07, 09:51 AM
#24
I have run a can of SeaFoam through 6 gallons of gas, while doing the H2O treatment and then I got through another 1/2 can of SeaFoam through a spray bottle down the carb primaries while revving it, and the car died from low compression.
I'm thinking that it's time to replace the motor with my 68k mile core.
I'm thinking that it's time to replace the motor with my 68k mile core.
08-13-07, 10:33 AM
#25
I've read more bad about ATF than good. I'd never put any in any of my engines. I don't even like puting it in a tranny (because I prefer manual, heh). Oh, and Steve was on the Mazspeed forum back in its heyday before this forum cranked up to speed. That's where the ATF 'treatment' essentially came from (unless it was discussed on the mailing list before, in which I never participated).
Now that that's out of the way, I did try MMO in my 20B right after I got it to attempt to loosen some sticky carbon on the apex seals. Back then in '03, nobody discussed the possibility of increased oil consumption and/or smoking issues from MMO use. I think it was known that ATF could cause it back then, so I knew to steer clear of it at least. I was also aware of the problems ATF can cause with the catalyitic convertor (something that Steve did not mention) as well as the appearant requirement to change your plugs after an ATF treatment (both of these drawbacks are listed in the 'facts' section on Mazspeed) and to drive it hard (not something I could do with the 20B then).
Anyhow MMO appearantly does not damage your cat or plugs if used in the same quantities as ATF. The MMO didn't damage the brand new plugs in my 20B, and I wouldn't have been happy if I needed to buy more.
The compression seemed to come up. The apex seals were no longer lazy in their slots. I did not have a compression guage but the engine did fire up reliably after hooking up the MegaSquirt. It starts with a puff of smoke and tends to smoke a little when the secondary injectors kick in. It however doesn't smoke on decel.
I'd say MMO is a winner and ATF should go away - it honestly causes more problems than it solves.
I have no experience with Seafoam other than the stuff in Puget Sound.
Now that that's out of the way, I did try MMO in my 20B right after I got it to attempt to loosen some sticky carbon on the apex seals. Back then in '03, nobody discussed the possibility of increased oil consumption and/or smoking issues from MMO use. I think it was known that ATF could cause it back then, so I knew to steer clear of it at least. I was also aware of the problems ATF can cause with the catalyitic convertor (something that Steve did not mention) as well as the appearant requirement to change your plugs after an ATF treatment (both of these drawbacks are listed in the 'facts' section on Mazspeed) and to drive it hard (not something I could do with the 20B then).
Anyhow MMO appearantly does not damage your cat or plugs if used in the same quantities as ATF. The MMO didn't damage the brand new plugs in my 20B, and I wouldn't have been happy if I needed to buy more.
The compression seemed to come up. The apex seals were no longer lazy in their slots. I did not have a compression guage but the engine did fire up reliably after hooking up the MegaSquirt. It starts with a puff of smoke and tends to smoke a little when the secondary injectors kick in. It however doesn't smoke on decel.
I'd say MMO is a winner and ATF should go away - it honestly causes more problems than it solves.I have no experience with Seafoam other than the stuff in Puget Sound.
Last edited by Jeff20B; 08-13-07 at 10:38 AM.